The world's energy consumption, even with improved conservation measures, is projected to triple, reaching approximately 46 trillion watts (TW) by the end of this century. With regard to future energy needs, it is noteworthy that 1.2×105 TW is deposited on the surface of the earth by the sun, in a broad IR to UV spectrum. The central energy challenge revolves around conversion, storage and efficient use of this immense solar power source.
Silicon-based solar cells supply the most reliable, cheapest and most common solution for high efficiency solar cells. It is therefore expected that solar cell farms will use some form of Si (amorphous, polycrystalline, or nanostructure) either as the active energy harvesting element, or as a substrate. Nevertheless, existing Si technology generating electric power is still about 3 times more expensive than energy from fossil fuels. A substantial improvement in Si-based solar cell efficiency is therefore essential.
The fundamental limits of solar energy conversion efficiency were explored by Shockley and Queisser for a p-n junction [1]. For an idealized p-n 1.3 eV bandgap junction, 30% maximum theoretical efficiency is predicted. Realistically, the p-n junction solar cell is limited by losses from a variety of sources including carrier thermalization and recombination, contact and junction losses and transparency losses. To date, the highest efficiency photovoltaic devices have been fabricated using multiple p-n junctions, the so-called tandem solar cells. The tandem cell efficiency record has recently exceeded 40% [2]. However, the requirements of lattice parameter and current matching between cells limit the development and increase the cost of the single cell.
Finding a simple way to couple organic layer to existing Si solar cells for increasing the cells' efficiency is of major importance. In this case, even an initial small improvement in cell efficiency of up to 3% would be useful. This improvement is an example of one possible application the system can achieve if quantum principles are exploited.
As the existing semiconductor technology shrinks in size beyond its current 45 nm, and as 22 nm fabrication technology is being developed, quantum nano-structures are likely to become the primary components of future electronic devices. Future revolution will create many opportunities for new engineering features. The fabrication of quantum devices is riddled with a number of major challenges and breakthroughs are required before a new generation of quantum electronics and logic operating devices are successfully produced. These challenges include device fabrication difficulties, which typically require micro- to nanometer scale resolution, de-coherence which erodes the operation of a quantum device, in addition to the resolution of crucial problems of control, such as manipulation and measurement of the quantum states in a device. Using a hybrid approach that applies quantum mechanical properties commensurate with simple classical measurement, may be the essential step towards using room-temperature quantum mechanics in real devices.
In several cases, nature uses quantum mechanics to achieve extraordinary results. A well-known example is the high photon conversion efficiency of photosynthetic light harvesting complexes, using coherence properties and quantum processes in the short scale. Recent experimental advances in various multi-chromophoric assemblies have raised the fascinating possibility that quantum coherent dynamics plays a role in photosynthetic energy transfer, even at room temperature [3-5]. Electron dynamics of bi-layered assembly [6] or a tri-layered assembly [7] of chromphors with different or equivalent energy gap structures, respectively, on a substrate have been discussed. These remarkable findings indicate that a key to the survival of quantum coherence in this temperature regime is the emergence of correlated energetic fluctuations between different chromophores, which are closely spaced, thus enabling the pigments to share the same coherent modes.